Antenna for automotive vehicles



April 7, 1959 J. B; BATCHELOR, JR 2,881,428

' ANTENNA FOR AUTOMOTIVE VEHICLES Filed Jan. 5, 1956 r 2 Sheets-Sheet 1A ril 7, 1959 'J. B. BATCHELOR, JR

ANTENNA FOR AUTOMOTIVE VEHICLES Filed Jan. 5, 1956 2 Sheets-Sheet 2 theloadingcoil is wound;

United States Patent ANTENNA FOR AUTOMOTIVE' VEHICLES Joseph B.Batchelor, In, Monroe, Ga., assignor, bymesue assignments,.to CentralElectronics, Incorporated, Chicago,-Ill., a corporation of IllinoisApplication January' 5, -1956, Serial No. 557,588.

2'Claims. (Cl. 343-714) The present invention rel'atesin general toantennas for transmitting radio signals, and in'particular'to adjustableinductance devices for tuning-"antennas used on automotive vehicles orothermobile equipment. The terms automotive vehicles is to be taken inits broadest sense inasmuch as antennas embodying the invention areadvantageously employed on passenger automobiles, trucks, tanks, smallboats and any other-moving conveyance.

It is the general aim ofthe invention. to provide an improved loading'or 'tuning inductance for antennas used on automotive vehiclesand whichmay-be .conveniently adjusted for substantiallyoptimum performance inany of a number of frequ'ency' ranges, while at the same timebeingfihighly efiicient in: its operation and small in sizeas well assimple-in construction.

Another object of thea-invention' is the provisionof such a-device whichmay be adjusted. for xoperationin diflferent' frequency ranges by meansoperable: from -a. .remote location, for example, the:driver-s:seat:ofan. automobile.

A further object is :to-"create :suchran :antenna in: which a loadingcoil, progressivelyshorted."forsioperationfof the antenna in differentfrequency ranges,is.so located as to give high transmission eificiencywith"regard to signal strength at distant points,1yet havingua coil. andswitching assembly of such compact size :that'it may be located in theposition'required'withoutan unduly large and heavy supporting structure;

It is still another object toprovide :ansantenna loading coil andswitchmeans .for adjusting the :same which are not only smalland compact, .butwhich successfully prevent arcing across ropeniswitchcontacts; present.negligible capacitance between .open switchrcontacts which mightotherwise adversely affect the operation; and which drastically reducethe undesirable eflects of mutual coupling between active-r-and.:.shorted.r coil portions.

Other -objectsxandtadvantages ofrthe invention .will become apparent as.thefollowingdescription proceeds, taken in conjunction withtheaccompanyingdrawings, in which:

Figure 1.is a.partial'side'elevation..ofa-:typical automotive vehiclehaving an antenna embodying, the features of the inventionmountedthereon;

' Fig. 2 is .an enlarged fragmentaryview, partially in section, of theantenna shown by. Fig.. 1;

Fig. 3 is a detail elevation-taken substantially along the line 3-3inFig. 1;

Fig. 4 is a vertical section .showinga coil andfswitchingassembly'employedin the antenna;

Figs. 5 and..6 are horizontal sections takem substantially alongthe.lines .55.'.and 6-6, respectively, ,in Fig. 4;

Fig. 7 is an enlarged fragmentary .section corresponding to a portion ofFig. 4 and illustrating. the manner in which Fig. 8 is a verticalsection. taken through the'lower portion of the antenna; and

Fig. 9'isan enlarged view-corresponding to a part of pacitive impedance.

tical matter to make'the antennaequal in physical length 2,881,428Patented Apr. 7, 1959 While the-invention has been shownand is describedin some detailwithreference to a'particular'embodiment thereof,there isno intention that itAthus-be limitedto such detail. On thecontrary, itis intended here to cover all alterations, modifications; andequivalents falling within the spirit and scope of theinvention'asdefined by the appended claims.

Referring now to the drawings, an antenna'10 constituting a preferredembodiment of .the invention'has been shown in Fig. l as mounted. on' anautomotive vehicle '11 which in this instance happens to be a 1conventional passenger automobile. The antenna-10 may be viewed as madeup of first and second elongated "electrically conductive: sectionswhich maybe-designated as the base section 12 and=the whipx14.Physically interposed between the base'12 and whip 14 is*a'loading-assembly 15 which, as explained in detail below, includes-an'inductance element orloadiiig coil connected inseries with the twoantenna sections. Assembly-15 may include a water-tight protectivecasing 16 coated onthe inside with a suitable insulating material 17 toreduce the possibility ofinadvertent electrical contact with theenclosed coil.

As shown best-in Fig. 2, the base 12 of the-antenna "is made as atubular steel member and is fixed in-a vertical position to, whileinsulated from, the vehicle 11. Forthis purpose, a support fitting "18is made fasttoa-panel"11a of =thevehicle by a plurality of bolts or.screws 19' which pass through insulating bushings --20="-insertedintomounting holes within thehousing; The screws 19 also pass through aninsulating ring .21 which may be made. of plastic or'other suitableinsulating'material Sothat-the fitting 18*and 'the antenna lllsupportedthereby are'both insulated from the-vehicle itself. The-lower-endof-=the base :section 12 isinserted'vertically dQWnWar-dintothe fitting18 and retained by suitable means such as set screws 22" (Fig. 3)threaded through the fitting-andengageable in openings 24 drilled in thebase: An arcuate cover plate 25 through which the *base12is'inserted'closes'the'top opening in the fitting 18 and is'drawntightly against the latter by an annular nut 26- engaged withthreads-cut onthe base itself.

For'feeding radio frequency"-'energy-to the antenna, a sheathed coaxialcable 27 leads fromwithin theinterior of the vehicle through anopening-27a cut in the'panelllh, the center conductor '27b beingelectrically: connected to the "base '12. The cable 27 may lead from :atransmitter (not shown) located.elsewhereiin thevehicle. For a purposeto be described, a rotatable torque transmitting cable 28' is extendedfrom within the vehicle through the insulating ring 21 'and an opening-'30 in'the-fitting itself.

Merely for purposes of illustration, it may b'e assumed that the antenna10 is to-be-oper-ated at signal: frequencies in the '10, 15 20, 40, andmeter bands; As is well known, the antennashould, when operating in eachband, approximate 'series'resonance or substantially correspond tosomeodd multiple ofa quarter-wavelength. Under these :conditions,maximum power is, drawn from the transmitterbecause the antenna presentsa low'impedance and also matches theiimpedance of the connecting coaxialcable. It is':possibleto -makethe antenna approximately-v physicallyequal to. an oddmultiple of a quarter-wave length .in' the highestfrequency range, .i.e., in-the- 10 meter band, but "asthe operatin'gfrequency-is lowered, the'antenna presentsa progressively higher 'ca- Ofcourse, it is impossible asapracto a'quarter-wave length in thelowest'frequency -range, i.e., in the 160 meter'band. And 'withrtheantennasubstantially less than aquarter wave length in-the lowerfrequencyranges; the capacitive impedance: which it :presents is sovery' high that little power is drawn fronr'the transmitter, and stillless is radiated'into space;

g It is well known that operation at the lower frequencies can beobtained by placing a coil in series with the antenna which has aninductance of proper magnitude to substantially resonate with theantennas capacity.-- A difierent value of inductance is needed foroperation in each frequency range, and in some cases for operation indifferent portions of one frequency range. This has led .in the past tothe use of a plurality of coils which might be substituted one for theother, or suitable coils having taps or contacts which could be adjustedto short out different portions.

In these prior arrangements, it was necessary for the operator to stopthe vehicle, disembark, and then either substitute coils in the antennaor adjust the tap of a coil mthe antenna, the latter steps oftenrequiring assembly .and disassembly of parts, by the use of tools.

Before considering that aspect of the invention which permits adjustmentof a loading coil from a remote locationand thus eliminates theinconveniences referred to, it will be appropriate to treat a secondfeature of the invention which concerns the physical location of aloading coil longitudinally of the antenna. It will be helpful ,to notefirst that all radiation in the communication frequencies is bothelectrostatic and electromagnetic in nature. The electrostatic radiationis commonly known as the ground wave and takes place through minute ca-;pacitive coupling between the antenna and foreign ob ects, such asreceiving antennas, located at remote points.

The electrostatic orground wave radiation is normally effective for onlyshort distances in the order of 3 to .miles and it is produced as theresult of voltage varia- .-tions on the antenna giving rise to aradiating electrostatic field. The electromagnetic radiation, on theother hand, is produced by current flow within the antenna generating achanging magnetic field which isradiated in --space. This is commonlycalled the sky wave and it is effective for extremely great distancesdepending upon .the atmospheric conditions.

In the loading coil for the antenna were located at its very base, orperhaps inside the body of the vehicle, it is possible to tune" theantenna to series resonance and thus properly load the transmitter.However, the result- ;ing current flow is primarily confined to theloading coil and is shielded by the vehicle body so that only a highvoltage is present, for practical purposes, on the exterior portion ofthe antenna. This produces then, a relatively strong electrostaticradiation or ground wave, and a -.correspondingly weak electromagneticradiation or sky wave. This has been proven by actual tests and foundunsatisfactory for transmission of signals over appreciable distances.

- On the other hand, if the loading coil is interposed and ,connected inseries with two antenna sections, the coil being located in the midportion of the antenna or near the top thereof, the upper portion of theantenna, for a given over-all length, becomes so short that it has verylittle capacity. As a result, in order to resonate that capacitivereactance an extremely large inductive loading tively heavy, coillocated near the top of the antenna has been found to present structuraldifiiculties. Either the base must be made unduly large and heavy, orrisk of breaking the antenna is present.

, to the lower portion of the antenna, which is capacitively coupleddirectly. back to the vehicle, that a relatively weak electromagneticwave is produced. If the loading coil is placed in the upper portion orcenter of the anstantially-perfectresonance is not readily t fib i vdcoil must be employed. Such a large, and therefore rela-' tenna then itmust be of higher inductance and since subassneas to the extremely smallcapacity of the shortened top antenna section, smaller currents flow inthe upper section of the antenna and thus produce a relatively weakelectromagnetic wave.

Accordingly, it has been my discovery proven by experiments that anelectromagnetic or sky wave" of maximum strength, for a given antennalength and transmitter power, may be obtained by locating the inductiveloading coil approximately mid-way between the center of the antenna andits lower end. Stated another way, I have found that appreciably betterradiation for long distance transmission can be obtained by making thecombined length of the antenna base section and the loading coilapproximately one-third as long as the upper antenna section, e.g., bymaking the'base 12 and loading assembly two feet long and the whip 14six feet long.

It has been my discovery that in order to obtain high transmissionefiiciency, the capacitive coupling between the upper portion of theantenna and the base or vehicle body must be maintained very low inrelation to the capacity between the upper antenna portion and freespace. In other words, stray capacity back to the vehicle body or theantenna itself which shunts radio frequency energy must be minimized inorder that substantially all of the radio frequency energy will beradiated, i.e., transmitted through the capacitance between the antennaand free space. For no matter how perfectly the antenna is tuned toresonance and how well it loads the transmitter, it is the strength ofthe transmitted signal which determines the success of the antenna.

Inputting this principle to advantageous use, a loading coil assembly isconstructed in a manner such that the stray capacity between itsadjacent turns is minimized, and switching means are provided whichpresent very little capacity across open contacts. These, two featuresresult in an antenna having a very small stray capacity between its whipand either the base or the vehicle, so that a greater proportion of theradio frequency energy is transmitted into free space.

In accordance with the invention, there is provided a loading assemblywhich due to its relatively small size and weight, is convenientlylocated as described above,

and which affords adjustment of the effective value of the loadinginductance by means operable from a remote location. In accomplishingthis, an elongated hollow coil form 35, having a central passage 36therethrough, is physically interposed between the base section 12 andthe whip section 14 (Figs. 2 and 4). As illustrated in the drawings, thecoil form 35 may be cylindrical in shape and may be made of any suitableinsulating material such as a ceramic. For attachment of its lower endto the upper portion of the base section 12, the coil form 35 iscounterbored and tapped at 38 to be screwed onto'threads cut in theupper extremity of the base section 12 (Fig. 4). Similarly, the upperend of the coil form 35 is counterbored and tapped at 39 to receive thethreaded shank 40 of a plug 41 having large spiral threads thereon. Forattaching the whip section 14 so that it may deflect without damage ifit should strike an overhead object, resilient means in the form of aheavyhelical spring 42 are employed. The spring has its turns inthread-like engagement with the plug 41, and receives at its upper endan externally threaded plug 44 which is internally tapped as at 45 toreceive the threaded lower end of the whip section 14. The base 12, coilform 35, and whip 14 are thus all supported in vertically upright,coaxial relation, the latter having freedom to deflect owing to theresiliency of the spring 42.

For providing the necessary compensating inductance in various ones ofthe frequency ranges, a coil designated collectively by the character 46is wound on the coil form 35. For optimum performance, the coil iscreated from a continuous conductor, or a number of conductor: connectedin series, which is wound in multiple'layei .z'between'the turns a :andb, lying'inzthe channel formed "thereby. After the turn iscompleted,;the wire is crossed ..axially:along the coil form and wrappedin a fourth turn .dudirectly in'contact with the coil form. The wireis'fthen crossed retrogressively. to form'the fifth turn e which If lieson and :between' the turns b and d. Upon-completion xxtofthe turn e, thewireisledaxially along the coil form ":to creat the turn f, 'andthenidoubled back to-form the tturn g lying overv and between the turns dand, f. The wire is, of course, enamel or otherwise insulated andthepattern illustrated by Fig. 7 is repeated over and over to create theentire .coil 46.

. Several advantages .have been .found to result from the acoil which isbank-woundas-described. Such-winding :lowers the. capacitive coupling:between adjacent turns,

i.e., the stray capacity across the coil. As .explainedabove, thiscontributes to the elimination of shunting energy. back to the base 12or the vehicle 11,so:that more :energy is radiated from the whipintofree space. Secondly, bank-winding increases the mutual: inductancebetween adjacent turns of the coil so that the coil has a higherinductance'for fewer turns, ascontrasted with a helical coil, therebypermittingit to be smaller in size. Moreover, fewer turns mean that ashorter length .of larger. diameter :coil wire. maybe used in theavailable :space so that copper-,losses,,i.e., 13R losses,'are consider-:ablyrreduced. As a result of the bank-winding arrange--:iment,:,ther'efore, azrelatively smallcoil provides a"relativelyhighxinductance with littlestray capacityand:resultsdnieflicientoperation since copper losses are con- :siderablyreduced.

,Asillustrated in Figs..2 and 4,the composite coil 46 is madenp of aplurality ofv individual "coil portions 5058-which are spaced :axiallyalong the :coil form. The several individual coil portions. spaced apartaxially may :be formed by a single conductor or-by a plurality ofindividual conductors which are connected-together. in .series relation.As noted, each of the coil portions 50-58 .:.is :bank-wound. Merely byway of example, the coil izportion 50 may present sufiicient inductanceto correctly resonate the antenna for operation in the 75. meter band.

Likewise, the sum of all of the inductances provided .by the'coilportions 50 through '58 properly'compensates for operation of theantenna in .the low portion of the 160 meter band. It will be observedthat the coil poreither the high, medium or low portion of the 160 meterband, while the coil portions 54 and 55 likewise provide forcompensating adjustment withinthe 75 ,meter band.

The coil form and coil are maintained relatively small in over-alldiameter while provision is made for pro gressively shorting out thecoil portions 50-58 to tune the antenna for operation in any of theseveral frequency bands indicated by way of example. For this purpose, aplurality of taps are electrically connected at spaced points along thecoil, and more particularly at junctions in the coil between thesuccessive coil portions. As shown in Figs. 2, 4 and 5, such taps arecre ated by electrically conductive screws 60 which are threaded into acorresponding plurality of radial holes drilled through the coil form35. The heads of the sev- .:-nect with the .coil conductor in'the'region where .itprogressesfrom one coil'portion toanother, asshownparticularly in Fig.2. The taps preferablyinclude resilient .brushes tofacilitate :switchingas described below.

In this instance, a small spring 61 of phosphor. bronze vor the like issuitably soldered or welded to the innerend of each screw 60, .theinner, free end161a .of the spring projecting into the passage .36.Electrical connection of thebase section 12 to the lowermostspring 61and screw 60, therefore, leaves all of the coil portion 50-58 in'series, while electrical connection of the base 12 toal1 of the springs61 and screws 60 shorts out each vof the respective coil portions 5058,leaving the antenna adjusted for proper operation in the 10 meter bandwith no compensating inductance.

The composite coil 46 is.electricallyinterposed orcon- .nectedbetweenthe base section .12 and the whip section :13. For this purpose, aconductive metal strap 65 (Fig. 2) is engaged by the top tap 'screw60anda screw '66 which is threaded through the coil form for lockingengagement and electrical contact with the shank 40 of the plug 41 (Fig.4). The .plug 41 is, of course, electrically connected with the whip 13through the spring 42 and the plug 44.

For the purpose of progressively engaging the coil taps here formed bythe springs61 and screws 60, a

conductive, preferably'non-magnetic plunger 70 is disposed withinthepassage 36 of the coil form 35 with freedom to slide axially therein..The plunger 70 is always electrically connected to the base. section12.regardless of its position, as will become apparent from thefollowing paragraphs. As itshupper end ismovedup- --wardly, itsuccessivelyengages the coil taps and there --load.a transmitter foroperation in the 15 meter band,

tions 57 and -58-permit adjustmenbfor' operation in "60.

fore successively shorts out the coil portions 58 through 50. With'theplunger 70 .in-theposition illustrated by Fig. 4, the coil portions 58,5.7, 56and-55 are all shorted andthe antenna is adjusted for operationin the high region of the 75 meter band. i

It will be observed that the cooperative arrangement of the coil tapsprojecting inwardly through the coil form and the plunger 70.slidableaxially within thecoilform results inanassembly whichis relatively smallin diameter. .Other advantages. accrue from the.arrangement-described.By spacing the coil portions 5058 axially apart onthe .coil form 35, thecoil taps formed by the screws 60 andsprings '61 are likewise spacedaxially apart. Thus. with the upper end ofithe plunger engaging a: givenone of the springs-(Slit still is considerably spaced from the next tapspring. there is very'little capacitive coupling between the upper .end'of the plunger 70 andthe next coil tap. Viewing For this reason,

theiplunger. 7i) and'each of the springs :61 as switch'contacts,therefore, the switch contacts have negligible capacity when open. Thusthe switchingarrangement min imizes capacitive shunting from the whipand activeportions'of. the coil back to the base. 12. This, as explainedabove, promotes greater efficiency by eliminating or minimizing shuntingof energy back to the base, to the end that most of the radiofrequencyenergy is radiated from the whip .into free space.

. Additionally, experience hassshown .that with theappli- .cation' ofonly 50 watts :ofxradio frequency energy to an :.antenna of this type,the voltage-becomes .so high that it will are approximately one-halfinch. I have found it necessary that open switch contacts be separatedby something in excess of one-half inch. In the present arrangement, theupper end of the plunger 70 is always separated from the next free coiltap by a considerable distance so that the likelihood of arcing issubstantially eliminated. Finally, with the coil portions spaced apartaxially on the coil form 35, there is only relatively small mutualcoupling between adjacent portions. This becomes important when oneconsiders the effect of shorted coil portions on unshorted coilportions. For example,

-as viewed in Fig. 4, theshorted coil portion 53 has relsmallcirculating currents are set up in the coil portion 53 and the powerloss in the latter coil portion, which would subtract from theefliciency of the antenna, is

minimized.

- In order to shift the plunger 70 to any of its axial positions, i.e.,to selectively short out successive ones of the coil-portions 50-58,motion transmitting means operable from a remote location are provided.In the present instance, the lower end portion 70a of the plunger 70 iscircular in shape and externally threaded. The upper end is preferablyrectangular in cross section to facilitate electrical contact with thesprings 61 and to prevent rotation of the plunger within the coil form.Cooperating with the externally threaded lower plunger portion 70a is aninternally threaded nut 74 which has a sliding, journaled contact withthe inner surface of the tubular base section 12. The nut 74 isrestrained against axial movement within the base 12 by a pair of retaining rings 75, 76 (Fig. 6) axially restrained inside of the base 12 bysuitable means such as inturned beads 12a. It will thus be seen thatrotation of the nut 74 in opposite directions serves to move the plunger70 up or down within the coil form 35. To prevent rotation of theplunger 70, it is passed through a bushing 78 seated in the upper end ofthe base 12 and having a rectangular hole 78a therethrough mating withthe cross section of the plunger 70 (Figs. 6, 8 and 4).

In order to effect rotation of the nut 74, it is rigidly socketed intothe upper end of an auxiliary tube 80 which is coaxially disposed withinthe base 12 and which coaxially surrounds the plunger portion 70a. Thetube 80 is journaled at its upper and lower ends by the retaining ring76 and a bearing ring 81, respectively. Disposed in the lower end of thetube 80 is a plug 82 having a non-circular opening therethrough whichreceives a non-circular or flattened end 28a of the cable 28, thuseffecting a driving connection between the cable and the tube 80.

The cable 28 as shown in Fig.) extends into the interior of the vehicle11 and may be rotated by any suitable means such as a hand crank, orpower means such as a motor. As here shown in Fig. 2, an electric motor'85 is located inside the vehicle and serves to drive the cable 28through a suitable speed reducing gear box 86.

The motor may be controlled for starting and stopping and as to itsdirection of rotation by appropriate switch means (not shown) located,for example, at the drivers seat. Through this arrangement, therefore,the operator of mobile radio transmitting equipment carried by thevehicle equipped with the antenna may adjust the latter for operation inany one of a number of frequency ranges simply by controlling therotation of the cable 28 and thus vertically positioning the plunger 70so that it engages a proper number of the tap springs 61 to short outthe proper ones of the coil portions 50-58. Yet, despite the convenienceafforded by this inductance-adjustingarrangement, the inductive coil andswich means are themselves so very compactly constructed that they maybe mounted, as indicated, physically interposed between top and bottomantenna sections. An especially high value of inductance is realized fora given size of the coil form and length of coil wire by bank-windingthe wire to create the composite coil 46. Such bank-windingsubstantially reduces capacitive coupling between adjacent coil turns,at the same time increasing mutual inductance between turns so that theover-all inductance of the coil portions is high relative to theirphysical size. The particular switch means consisting of taps projectinginwardly from the coil to the interior of the coil form and cooperatingwith an axially movable plunger, results in a switching means whichleaves the coil assembly small in diameter but yet which presentsnegligible capacitance between open switch contacts, and spaces thoseopen contacts sufficiently to prevent arcing when the antennais drivenwith relatively high power.

I claim: t

1. For use with an antenna having two conductive sections, one of saidsections being hollow and rigid and having means for attaching the samein a vertical position to and insulated from an automotive vehicle, thecombination comprising a hollow elongated coil form of insulatingmaterial rigidly fastened in vertical position to the upper end of saidone section, spring means fastening the other of said antenna sectionsin vertical position to the upper end of said coil form, a coilcomprising wire bank-wound on said coil form in serially connectedportions spaced apart axially of the coil form, means electricallyconnecting the extremities of said coil respectively to said two antennasections, a plurality of coil taps connected respectively with the wirebetween successive ones of said coil portions and extending inwardly tothe interior of said coil form, a conductive plunger having electricalconnection with said one antenna section and slidable axially withinsaid one section up into said coil form to contact said taps andsuccessively short out said coil portions, means rotatably disposedwithin said one antenna section and connected with said plunger forshifting the latter axially, and a flexible drive connection leadingfrom the exterior of said one section to said rotatable means forturning the latter.

2. For use with an antenna mountable on an automotive vehicle, thecombination comprising a base section of tubular metal, a hollowcylindrical coil form of insulating material and means fixing it incoaxial relation to one end of said base section, a coil made up by aconductor bank-wound upon said coil form in series connected axiallyspaced portions, a plurality of taps ex tending through said coil formand electrically connectec' to said coil intermediate the successiveportions thereof, 2 conductive r'od slidably extending through said coiltorn and adapted to engage said taps, the lower end of saic rodprojecting into said hollow antenna section and hav ing threads thereon,a nut disposed within said hollov antenna section and threadably engagedwith the lowe end of said rod, and means including a flexible elemenextending from the interior of the exterior of said hollov section forrelatively rotating said nut and rod, so that th! rod may be movedaxially to progressively contact sail taps and short out successive onesof said coil portions.

Hefele Sept. 14, 194 ElllS Oct. 4, 195

